Synthesis And Photocatalytic Performance Of ?GaN?_1-x?ZnO?_x Nanostructures With Morphology And Band Gap Tailoring

Semiconductor photocatalysis including photocatalytic degradation,photocatalytic water splitting and photocatalytic reduction of CO2 has been considered as an effective and promising strategy for tackling the aspects of energy and environmental crisis on basis of clean solar energy.The core issue in this filed is how to develop highly efficient and stable photocatalyst with more light absorption and active sites.(GaN)1-x(ZnO)x solid solution as a promising photocatalyst has attracted extensive attentions due to its excellent visible light absorption and photocatalytic overall water splitting for H2 production.As ZnO(3.2 eV)substitutionally solubilizes into GaN(3.2 eV),its band gap can be selectively tuned from 3.4 to 2.2 eV by controlling ZnO content.However.previous research work was mainly focued on the bulk-form(GaN)1-x(ZnO)x solid solution sintered by micro-crystals in which the long migration path of photogenerated carriers and a large number of structure defects arisen from solution process dramatically reduced the recombination efficiency of photogenerated electrons and holes and thus decreased the entire photocatalytic activity.To solve aforementioned problems,in this thesis,we mainly focus on the synthesis of(GaN)1-x(ZnO)x solid solution nanostuctrues and try to decrease the recombination efficiency of photogenerated carriers and further improve visible light absorption and active sites for the purpose of achieving superior photocatalytic activity.At first,we combined a sol-gel method and nitridation process to successfully prepare porous(GaN)1-x(ZnO),solid solution nano-powders with a tunale band gap of 2.38-2.76 eV and corresponding ZnO content of 85-25%.Their photocatalytic degradation performance was systematically investigated by removing phenol pollutants.It was demonstrated that there existed an optimal band gap structure with a balance between the visible light absorption and redox ability of photogenerated carriers.Among them,(GaN)0.75(ZnO)0.25 solid solution achieves the highest photocatalytic performance compared to the other samples due to its higher redox ability,more visible light absorption and lower structure defects.A slight of Ag decoration can effectively improve the surface electron transfer efficiency and photocatalytic performance.In particular.1 wt%Ag decoration leads to a 10 times reaction rate faster than that of pristine(GaN)0.75(ZnO)0.25.Phenol in aqueous solution(10 mg L-1)can be completely degraded within 60 min under the direct exposure of sunlight,demonstrating the promising photocatalytic ultilization of(GaN)1-x(ZnO)x solid solution in environmental processing.A in-situ CVD method was also developed to synthesize one dimensional(GaN)1-x(ZnO)x solid solution nanorods with higher crystal quality and smaller size on the purpose of decreasing the recombination efficiency of charge carriers.By carefully controlling the growth temperature and nitridation time,we realized the crystallographic facet tailoring of(GaN)1-x(ZnO)x solid solution nanorods from non-polar {10-10} to semipolar{10-11} and then finally to mixed {10-11} and polar {0001} for the first time.The corresponding CL analysis demonstrated that(GaN)1-x(ZnO)x solid solution nanorod with ZnO content of 95%,80%and 25%possessed obvious visible light emission.Their corresponding band gaps were roughly estimated to be 3.02 eV,2.95 eV and 2.75 eV on the basis of near band edge emission.It proves that increasing ZnO ratio from 0 to 1,the band gap of(GaN)1-x(ZnO)x solid solution would decrease first and then increase,matching well with the theoretical prediction.The efficiency and versatility of our strategy in the facet engineering will opens up more opportunities on further enhancing the photocatalytic activity of(GaN)1-x(ZnO)x solid solution nanostructures.Then,taking full advantage of the confinement effect of Au nanoparticles,we further decreased the size of 1D nanostructures and obtained(GaN)1-x(ZnO)x solid solution nanowires with a diameter of 50 nm and length up to 2 ?m.The ZnO content and band gap of(GaN)1-x(ZnO)x solid solution nanowires can be selectively tailored from?10%to?35%and 3.08 eV to 2.77 eV through the use of Zn-Ga-O precursors with different Zn contents ranging from 10%to 60%.Additionally,it was demonstrated that the formation of Au-Ga alloy catalyst played an important role in the Au-assisted VLS nucleation and growth mechanism of(GaN)1-x(ZnO)x nanowires.The PEC measurements show that(GaN)1-x(ZnO)x solid solution nanowires as photoanodes can realize the overall water splitting at a voltage lower than 1.23 V vs RHE and the corresponding photocurrent density is gradually increased with the reduce of band gap and finally reaches to?30 ?A cm-2.Finally,we proposed a two-step reactive template route to successfully prepare 2D(GaN)1-x(ZnO)x solid solution nanosheet with ultrathin thickness of 14 nm.The atomic structure model analysis and experiment results verified that<111>-oriented 2D ZnGa2O4 nanosheets can be perfectly converted to<0001>-oriented 2D(GaN)1-x(ZnO)x solid solution nanosheets with the minimum distortion energy and shortest atomic diffusion path.The transformed 2D(GaN)1-x(ZnO)x nanosheet excellently maintain the initial hexagonal morphology and single crystal characteristics of ZnGa2O4 nanosheet template except to a certain degree of edge breakage and surface roughness as well as pores formation.The 1wt%Rh co-catalyst modification on the surface of(GaN)0.89(ZnO)0.11 nanosheets with band gap of 2.77 eV directly results in clearly observed H2 evolution of 0.7 pmol h1-g-1 in an aqueous H2SO4 solution,suggesting the occurrence of water decomposition.